The fetal cardiovascular function in chronic placental insufficiency is different from experimental hypoxia.

Ten mothers at normal term pregnancy were rendered mildly hypoxic by allowing them to breathe a gas mixture of 10% oxygen and 90% nitrogen. The fetuses were studied with Doppler ultrasound and computer assisted cardiotocography. There was vasodilatation in the cerebral vasculature while the utero-placental blood flow decreased. No changes in fetal haemodynamics occurred. The fetal heart rate was correlated inversely to the heart rate variation. There was a positive correlation between the heart rate variation and the umbilical flow velocity waveform index. In a group of 30 subjects with severe pre-eclampsia and/or severe intrauterine growth retardation, the fetal heart rate variation was inversely correlated to the umbilical blood flow. Hence, the study shows a clear physiological difference in fetal heart function during short-term hypoxia compared to that during long term placental insufficiency.